The present invention relates, in general, to track survey methods, and more specifically to a method of surveying a track, in which a first and a second measuring vehicle are positioned at end points, respectively, of a track section to be measured during a measuring cycle, the first measuring vehicle being designed for mobility independently of the second measuring vehicle which is stationary during the measuring operation, and the position coordinates of the second measuring vehicle are determined, a reference line in the form of an optical measuring beam is set up between the two measuring vehicles, and the mobile, first measuring vehicle is advanced in the direction towards the stationary, second measuring vehicle while any change in position of a receiving unit, mounted on the first measuring vehicle, relative to the reference line is registered as a correction measurement value.
A method of track surveying with a track pre-measurement car called EM-SAT is described in the publication “Der Eisenbahningenieur” (“The Railway Engineer”), May 1995, pages 314 to 318. The measurement operation is carried out in a cyclical fashion. The measuring vehicle (also called satellite) which is stationary during the surveying operation is first moved along the track in the operating direction until it is close to the next geodetically surveyed reference point, normally located on a catenary mast. A laser beam emitter mounted on the satellite is aligned with regard to said reference point, adjoining in the transverse direction of the track, and thus is brought into an exact desired position. Thereafter, with the aid of a telescope fastened to the laser beam emitter, the latter is aligned with a receiver located on the main machine which constitutes the other, mobile measuring vehicle. During this, the measuring axle of said mobile measuring vehicle is stopped exactly at a reference point which has previously been marked with paint at the rail base. This precise positioning is facilitated by a video camera showing the rail base and the wheel of the measuring axle.
The actual surveying of the track section is initiated by advancing the mobile measuring vehicle, with the position of the laser beam relative to the actual position of the track being measured at intervals of 20 centimeters and stored. With the aid of a special computer program it is possible to calculate from the geometrical data in a track monument plan the desired versines for line and level. To do this, it is merely necessary to input the track geometry and the position of the reference points. These versine values serve for comparison to the measured versines, with the difference thereof producing the correction values for level and line. The surveying of the track section is finished as soon as the mobile measuring vehicle has reached the stationary measuring vehicle. While the stationary measuring vehicle is advanced to the next reference point in order to carry out the succeeding measuring operation, the displacement- and lifting values for the just surveyed track section are computed. The determined correction values may be stored on a floppy disk to be loaded into a tamping machine, for instance, and to be worked off automatically for the accurate correction of the track position.
U.S. Pat. No. 5,493,499 describes a method of surveying a track wherein two measuring units, movable on the track, are placed at both end points of a track section to be measured and their respective positions are defined in relation to a track reference point. Subsequently, one of the two measuring units is moved in steps in the direction towards the other measuring unit, wherein, at every interruption of travel for implementing a measuring procedure, the measurement data of the actual track position are compared with the measurement data of the desired position and a corresponding differential value is calculated and stored. In this, as a result of the reception of a position signal from surveying satellites (Global Positioning System or GPS), the position of the two measuring units relative to one another in a coordinate system is determined. At each stop of the second measuring unit during its measurement travel in the direction towards the opposite, first measuring unit, the respective relative change in position is determined as a result of the reception of a further position signal from surveying satellites.
Additional details regarding the said methods of track surveying are described in the publication “Der Eisenbahningenieur” (“The Railway Engineer”), August 1995, pages 560 to 563.
According to an article called “GPS-based data collection” in the publication “Railway Age”, December 1994, pages 66 and 67, it is known to use GPS to determine which track sections require treatment.
Finally, a method and a device for rapidly and accurately determining the position coordinates of a movable receiver relative to a fixedly installed receiver are described in U.S. Pat. No. 4,812,991.